How Stress Becomes Depression

How Stress Becomes Depression

Depression is an everyday experience for many.  About 15% of the population struggle with its crippling effects at any given time.  For years, depression has been defined as a chemical imbalance in the brain.  While that is still true, we are finding more and more that the chemical imbalance is a result, not a cause of depression.  Current research is increasingly suggesting that most depression is caused by the effects of chronic stress, which shrinks both the hippocampus and the prefrontal cortex in the brain, which together are called the “executive” part of the brain.  But how does stress cause depression?

A recent journal article explored the effects of stress on dopamine in mice.  The hormone dopamine is related to our experience of pleasure.  So the researchers would put a new object in a mouse’s cage–for example, a ball.  When the mouse encountered the object, and explored it, the mystery of the strange object caused the release of a molecule called CRF in a specific part of the brain called the nucleus accumbens, which in turn released dopamine.

They thought that CRF was the key, so they experimented with it and yes, it had reinforcing properties, which would cause a mouse to return to an area of the cage where it had been given extra CRF.  And CRF also caused the release of dopamine, which led to the experience of pleasure.  Here’s the interesting part.  Now when a mouse was exposed to major sustained stress for several days, CRF flipped and did the opposite–there was no release of dopamine.  Instead it now triggered the release of stress hormones.

As a consequence, the mouse started to experience a depressed mood.  There was no more experience of pleasure.  Stress not only stopped the release of dopamine, it went the other way.  It was like a switch had been flipped.  Now the mouse would avoid formerly pleasurable places in the cage, and was not interested ini any novel object put into its cage.

One of the symptoms of depression is called anhedonia, which means one no longer experiences pleasure   The study inferred that the same thing happens in us when we are exposed to prolonged stress.  The CRF in our brains will begin to work in opposition to how it used to work and we not only no longer experience pleasure, we don’t even want to pursue it.

That’s why exercise is so important when we are depressed.  Exercise and sleep are the two ways we get rid of the stress hormones. including glucocorticoids.  It’s not easy, for the person struggling with depression doesn’t want to exercise, and they aren’t sleeping very well.

That’s also why depression is so crippling.  You can’t tell a depressed person to “just pull yourself together” for there is a process going on in their brain that doesn’t respond to “just pulling oneself together.  This comes from the new understanding in brain science and it underscores prolonged stress as the cause of most depressions.You can read more on this in my book Rethink How You Think.

Question:  If stress is the major cause, how does one avoid and/or combat depression?